This invention relates to biodegradable packaging material derived from high amylose starch and to the method of preparation thereof.
Problems associated with the handling of environmental waste, particularly the large amount of discardable plastic products and the limited volume of land fill facilities, has placed added emphasis on developing products which are either biodegradable or recyclable. This is particularly true in the packaging areas where large volumes of discardable plastic packaging materials are used in various forms, including containers, sheets, films, tubing and fillers. Because of this large increase in the use of plastic materials, it has been proposed to make throwaway materials from biodegradable plastics to alleviate the waste disposal problems. Several reasons have prevented the development and likelihood of developing this technology except in special situations. First of all, the high volume packaging plastics such as polyethylene, polystyrene, polypropylene and polyethylene terephthalate are low cost and are not biodegradable. Attempts to make such materials biodegradable by blending them with biodegradable fillers or additives have not been overly successful. Those existing plastics which are biodegradable, are deficient in properties required in most packaging applications and are more expensive than commonly used packaging plastics. Degradable plastics are more difficult to recycle than nondegradable plastics. Furthermore, another reason the nondegradable plastics are preferred in landfill sites is because they do not generate noxious or toxic gases.
Starch, a readily available, known biodegradable material, has been used to prepare foamed and film products as well as other shaped products for different purposes including selected packaging applications. In Patent Cooperation Treaty (PCT) Publication No. WO 83/02955, a foamed starch product is formed by extruding starch in the presence of a gas expanding agent, the product being useful in various applications such as foam sheets or fillers for packing.
The use of starch materials to form film products is well known, as shown e.g., in British Patent No. 965,349 which discloses the extrusion of amylose material without using solvents, to form films having excellent tensile strength. Another film forming operation using starch is shown in U.S. Pat. No. 3,116,351 where an unsupported amylose film is made by extruding an aqueous alkali-amylose solution into a coagulation mixture of ammonium sulfate and sodium sulfate.
U.S. Pat. No. 4,156,759 discloses a process for preparing low cost polyurethane foam by incorporating a starch containing amylaceous material into the foamed material yielding rigid or flexible and high resilient products.
U.S. Pat. No. 3,137,592 shows the extrusion of starch to produce an expanded gelatinized product in different shapes and forms, such as ribbon, ropes and tubes, which are useful in a variety of applications.
U.S. Pat. No. 3,336,429 involves a method for producing clear, thin. elongated shaped structures of amylose in forms such as film, tubes, bands and filament, by extruding an aqueous caustic solution of high amylose material through an aqueous acid bath.
U.S. Pat. No. 3,891,624 discloses the preparation of a dispersible, hydrophobic porous starch product by extrusion of a selected hydrophobic starch material at a temperature of 100.degree. to 250.degree. C. and a moisture content of 4 to 15 percent.
The use of starch in foods and confectionery products is well known. One area where starch use has been of particular interest involves expanded products such as snack foods and dry pet foods. The quality of such products, as evidenced by their crispiness, is affected by expansion volume which was studied and reviewed in two recent articles by R. Chinnaswamy and M. A. Hanna: "Relationship Between Amylose Content and Extrusion-Expansion Properties of Corn Starch", Cereal Chemistry, Vol. 65, No. 2, 1988, pp. 138 to 143 and "Optimum Extrusion-Cooking Conditions for Maximum Expansion of Corn Starch", Journal of Food Science, Vol. 53, No. 3, 1988, pp. 834 to 840.
The use of starch in the manufacture of confectionery products is disclosed in U.S. Pat. No. 3,265,509 where a mixture of high amylose starch and sugar is passed through an extruder in the presence of less than 25% moisture, to form a solid, plastic, shape-retaining confectionery mass.
While the disclosures noted above show the use of amylose containing starch materials in forming films and various other shaped products, the use of such materials in packaging has generally been limited to selected applications such as film wrappings for food. The area involving resilient, compressible, low density packaging materials for uses such as protective packaging, has been generally left to lightweight plastics, including expanded polystrene, more particularly Styrofoam (registered trademark of Dow Chemical Co.). However, as noted earlier, these materials are not biodegradable and, therefore, the need still exists for a material which will meet the demanding requirements of the packaging industry while satisfying the ever increasing governmental regulations and controls for environmental waste.